PITTSBURGH — Pittsburgh police say an alleged drug deal at the county public defender’s office in January is part of a larger problem not at that office, but with blatant, open-air, low-level drug dealing downtown. Police held a news conference today to discuss charges reported earlier this week against two men allegedly involved with selling prescription anti-anxiety pills to an undercover cop. But while police say the deal in the defender’s office appears to be an isolated incident there, it’s part of a larger problem targeted by charges being filed against 34 people in what police are calling “Operation: Revolving Door.” The round-up is so named because much of the dealing centers on people coming and going from a downtown McDonald’s restaurant, which has been identified by law enforcement officials in the past as a hub of drug activity.